fix sigsegv in query.c:filter_sourcerpm().
fix sigsegv in query.c:filter_sourcerpm().

Reported by <mgracik@redhat.com>.

Triggered when filtering by sourcerpm and the sourcerpm package itself is in the
Sack too.

yavor-atanasov/hawkey,cgwalters/hawkey,Conan-Kudo/hawkey,ignatenkobrain/hawkey,jsilhan/hawkey,rpm-software-management/hawkey,jsilhan/hawkey,megaumi/hawkey,mizdebsk/hawkey,MichaelMraka/hawkey,ignatenkobrain/hawkey,ignatenkobrain/hawkey,yavor-atanasov/hawkey,rpm-software-management/hawkey,rholy/hawkey,megaumi/hawkey,Conan-Kudo/hawkey,MichaelMraka/hawkey,mluscon/hawkey,MichaelMraka/hawkey,rholy/hawkey,mluscon/hawkey,jsilhan/hawkey,mizdebsk/hawkey,MichaelMraka/hawkey,ignatenkobrain/hawkey,mluscon/hawkey,megaumi/hawkey,cgwalters/hawkey,rholy/hawkey,Conan-Kudo/hawkey,rpm-software-management/hawkey,megaumi/hawkey,cgwalters/hawkey,cgwalters/hawkey,mluscon/hawkey,rholy/hawkey,yavor-atanasov/hawkey,jsilhan/hawkey,mizdebsk/hawkey,rpm-software-management/hawkey,Conan-Kudo/hawkey,mizdebsk/hawkey,yavor-atanasov/hawkey